The life cycle of Bunoderella metteri Schell, 1964, an intestinal parasite of the tailed frog, Ascaphus truei Stejneger in the Pacific Northwest, is described. Eggs are unembryonated when laid. Miracidia do not hatch in water. Ophthalmoxiphidiocercariae develop in rediae in the fingernail clam, Pisidium idahoense Roper. Larvae and pupae of the caddisfly, Rhyacophila grandis Banks, and dipterous larvae of the family Chironomidae serve as hosts for the encysted metacercariae. Immature specimens of B. metteri were recovered from the intestine of experimentally infected, laboratory-reared Rana aurora Baird and Girard, and Ascaphus truei. The only known bunoderid life cycle is that of Bunodera luciopercae (Miiller, 1776) Liihe, 1909, an intestinal parasite of freshwater fishes, reported by Wisniewski (1958). In Europe the cercariae develop in rediae in the freshwater clams Sphaerium corneum Linn. and S. rivicola Lamarck, and encyst in several species of Cladocera and Copepoda. Fishes become infected by ingesting the infected crustaceans. This paper presents the life cycle of an additional species. Bunoderella metteri Schell, 1964, is an intestinal parasite of the tailed frog, Ascaphus truei Stejneger, in the Pacific Northwest. Studies on its life cycle were undertaken concurrently in Idaho and Oregon. MATERIALS AND METHODS Adults of Ascaphus truei were collected at night from cold mountain streams in northern Idaho, western Oregon, and eastern Washington. The frogs remained alive many weeks when kept in water at 40 to 50 F. The water was changed every few days and saved as a source of parasite eggs that had passed in the feces of the host. Eggs collected by the sedimentation technique were placed in petri dishes on moist filter paper. Larval stages of the parasite were studied alive. Vital dyes (neutral red and Nile blue sulphate) were used to observe gland and flame cells of the cercariae. Naturally infected first intermediate hosts, Pisidium idahoense Roper, were collected from the same localities. The clams were kept alive for many weeks in dishes containing cold stream water and Received for publication 14 December 1964. * School of Natural Sciences, Arizona State College, Flagstaff. t Department of Biological Sciences, University of Idaho, Moscow. + Department of Zoology, Oregon State University, Corvallis. about 0.5 inch decaying vegetation. Measurements are in microns unless otherwise indicated.